Date: Mon, 14 Oct 2024 17:15:18 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Greg Sabino Mullane <htamfids@gmail.com>
Cc: Dagfinn Ilmari =?utf-8?Q?Manns=C3=A5ker?= <ilmari@ilmari.org>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Changing the default random_page_cost value
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On Mon, Sep 30, 2024 at 10:05:29AM -0400, Greg Sabino Mullane wrote:
> On Fri, Sep 27, 2024 at 12:03 PM Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
> wrote:
> 
>     It might also be worth mentioning cloudy block storage (e.g. AWS' EBS),
>     which is typically backed by SSDs, but has extra network latency.
> 
> 
> That seems a little too in the weeds for me, but wording suggestions are
> welcome. To get things moving forward, I made a doc patch which changes a few
> things, namely:
> 
> * Mentions the distinction between ssd and hdd right up front.
> * Moves the tablespace talk to the very end, as tablespace use is getting rarer
> (again, thanks in part to ssds)
> * Mentions the capability to set per-database and per-role since we mention
> per-tablespace.
> * Removes a lot of the talk of caches and justifications for the 4.0 setting.
> While those are interesting, I've been tuning this parameter for many years and
> never really cared about the "90% cache rate". The proof is in the pudding: rpc
> is the canonical "try it and see" parameter. Tweak. Test. Repeat.

I am not a fan of this patch.  I don't see why _removing_ the magnetic
part helps because you then have no logic for any 1.2 was chosen.  I
would put the magnetic in a separate paragraph perhaps, and recommend
4.0 for it.  Also, per-tablespace makes sense because of physical media
differences, but what purpose would per-database and per-role serve? 
Also, per-tablespace is not a connection-activated item like the other
two.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  When a patient asks the doctor, "Am I going to die?", he means 
  "Am I going to die soon?"